1. Field of the Disclosure
The disclosure relates to a process for separating solids from a purification purge stream, and more particularly to a process for removing impurities comprising vanadium and/or hydrocarbon residues from a purification purge stream comprising titanium tetrachloride and the impurity.
2. Description of the Related Art
Titanium tetrachloride obtained by reacting titanium-containing ore with chlorine can contain impurities comprising chlorides of iron, silicon, tin, aluminum, vanadium, chromium, niobium (columbium), tantalum, tungsten, tin, zirconium, etc., resulting from the corresponding metals present as impurities in the ore. Of these impurities the most significant is vanadium, because there is only approximately a 9° C. difference between the boiling point of its chloride and that of titanium tetrachloride causing it to vaporize at approximately the same temperature as titanium tetrachloride making it difficult to separate. Vanadium is a valuable material, but it is difficult to recover economically.
After preliminary separation from higher boiling impurities, crude titanium tetrachloride is subjected to chemical purification to remove vanadium. In this chemical purification step, a reagent is added that removes dissolved vanadium into a solid phase, generally together with a residue of the reagent. Separating purified titanium tetrachloride leaves behind a slurry containing the solids, which must be purged from the purification step. Currently, purge titanium tetrachloride from purification comprising vanadium solids is recycled back to the preliminary separation step, which mixes those solids with the higher boiling impurities, and may result in the re-chlorination of the vanadium solids formed in the purification step as well as the formation of Persistent, Bio-accumulative, and Toxic (PBT) organic compounds from hydrocarbon residues.
A need exists for a robust process for the separation of vanadium chloride from the titanium tetrachloride formed in the chlorination process, and for removal of any hydrocarbon residues that may be formed during the purification step.